The term substance use disorder encompasses both dependence on and abuse of drugs (e.g., depressants, stimulants, opioids, cannabinols, hallucinogens, inhalants) usually taken voluntarily for the purpose of their effect on the central nervous system (e.g., intoxication or high) or to prevent or reduce withdrawal symptoms (Diagnostic and Statistical Manual of Mental Disorders, 4th edition, American Psychiatric Association, Washington D.C., 1994). These maladaptive patterns of substance use in and of themselves lead to significant impairment and distress. In addition, substance abuse and dependence may worsen preexisting medical conditions and/or mimic other types of medical or psychiatric problems. The lifetime prevalence of substance use disorders including alcoholism is on the order of 20% for men and 15% for women, with young adults and middle-aged persons most heavily affected (See, e.g., Schuckit, “Drug Abuse and Dependence,” in Scientific American Medicine, vol. 3, chapter 13, section IV, pp. 1-12, 2004). Importantly, substance abuse related conditions are estimated to reduce the life span of a dependent individual by some ten or more years (Schuckit, supra, 2004). In fact, in the United States, over 100,000 deaths/year are directly attributed to alcohol use (O'Connor, “Alcohol Abuse and Dependency,” in Scientific American Medicine, vol. 3, chapter 13, section III, pp. 1-9, 2001). Substance abuse not only impinges on the health of the drug abusing individual, but also affects other members of society through drug use related accidents, crime, etc.
The identification of individuals who are heavily consuming alcohol or other licit (e.g., tobacco) or illicit drugs, as well as the ability to monitor those individuals who are receiving treatment for dependence, requires objective biochemical markers of alcohol or drug use. Most drug screens use urine samples, however for a result to be positive a subject must have taken the substance in question recently (e.g., hours, or at most, days). Thus, a sample from a subject with a severe, chronic substance use problem, may test negative if the subject is able to refrain from using the substance for only one or two days preceding the toxicology screen. Moreover, typical urine tests simply indicate the presence or absence of a drug or its metabolite, and do not provide any information regarding the quantity or pattern of drug use.
Thus, there remains a need in the art for methods and test kits for assessing drug use, abstinence and/or relapse. In particular, the identification of stable biomarkers that are reflective of chronic, heavy substance use and/or occurrence of relapse are desirable for development of improved diagnostic tools.